A general purpose computer uses a central processor unit (CPU) to perform instructions on data. The instructions to be executed and the data required by those instructions are read from a computer memory. The overall speed of the computer is affected both by the speed at which the CPU can execute instructions and the speed at which the memory can provide instructions and data to the CPU. To improve the speed at which instructions and data are supplied by the memory, modem computers often issue and complete memory transactions speculatively. That is, the processor predicts what instructions and data are likely to be needed in the near future and the memory is accessed to obtain instructions and/or data prior to the actual requirement for the speculatively accessed memory contents.
Computer memories are subject to a variety of transient failures that result in corruption of the content of a particular memory location. While such transient corruption is infrequent, the consequences of such corruption, particularly if the content represents an instruction to be executed, can be catastrophic to the proper execution of a computer program. Computers may include means to detect errors in the contents retrieved by a memory access. There may be further means to correct at least some detected errors. Such error detecting and correcting means generally introduce a substantial delay in the processing when an error is detected. Uncorrected errors may require abnormal termination of an executing program. Simplicity and low-cost in error recovery processing is favored over speed because memory errors are encountered infrequently.
In a computer that uses speculative memory accesses, memory errors may be detected during a speculative memory access. A significant proportion of the memory accesses may be speculative accesses in a computer that uses speculative accesses. A significant proportion of the speculative accesses may be for memory contents that will not be used by the CPU during the time the contents are available from the speculative access. The delays introduced by the error recovery processing for speculatively accessed corrupted memory contents adds an unnecessary overhead when the contents are not actually required by the CPU. An uncorrectable error detected during a speculative access can cause a potentially unnecessary abnormal termination of an executing program.